1. Field of the Invention
The present invention relates to an ATM switching system, and in particular, to an ATM switching system capable of servicing N-ISDN traffic and a method for controlling the same.
2. Description of the Related Art
Since an ATM (Asynchronous Transfer Mode) technology was adopted as a principal technology for realizing B-ISDN (Broadband-Integrated Services Digital Network), various communication equipment employing the ATM technology have been put on the market. According to the state of the art, the ATM technology can service N-ISDN (Narrowband-ISDN) traffic through an ATM network. Though many efforts have been made to service the N-ISDN traffic using the ATM technique, it is not yet possible to provide the voice subscriber with a satisfactory service, since the ATM technique is different from the existing circuit switching (or line switching) technique in the data transfer mode. Therefore, in a transition period, the ATM switching system requires an additional function for servicing the N-ISDN traffic.
At present, many efforts have been made to provide voice service to the subscriber connected to a public switched telephone network (hereinafter referred to as a PSTN) by means of an interworking device disposed between the PSTN and the ATM network. However, in this case, a time delay problem and a lowered cell transfer efficiency problem (i.e., a lowered bandwidth efficiency problem) are caused, when N-ISDN traffic data output from the PSTN is assembled into an ATM cell.
The following patents each disclose features in common with the present invention but do not teach or suggest the specifically recited ATM switching system for supporting N-ISDN traffic and a method for controlling the same in accordance with the present invention: U.S. Pat. No. 5,375,118 to Rao et al., entitled Apparatus For Transmitting Data Between Two Parties Belonging To At Least One Narrow Band Integrated Services Digital Network, U.S. Pat. No. 5,623,491 to Skoog, entitled Device For Adapting narrowband Voice Traffic Of A Local Access Network To Allow Transmission Over A Broadband Asynchronous Transfer Mode Network, U.S. Pat. No. 5,608,447 to Farry et al, entitled Full Service Network, U.S. Pat. No. 5,638,364 to Sugita, entitled ATM-LAN With CLSF Processor And Simplified CLAD Units, U.S. Pat. No. 5,742,765 to Wong et al., entitled Combination Local ATM Segmentation And Reassembly And Physical Layer Device, U.S. Pat. No. 5,737,312 to Sasagawa, entitled Cell Assembly And Disassembly Apparatus In AN ATM Network, U.S. Pat. No. 5,610,921 to Christensen, entitled Scalable Architecture For Asynchronous Transfer Mode Segmentation And Reassembly, U.S. Pat. No. 5,541,926 to Saito et al, entitled A TM Cell Assembly And Disassembly Device With Enhanced Data Handling Flexibility, U.S. Pat. No. 5,390,175 to Hiller et al, entitled Inter-Cell Switching Unit For Narrow Band ATM Networks, U.S. Pat. No. 5,214,642 to Kunimoto et al., entitled ATM Switching System And Adaptation Processing Apparatus, U.S. Pat. No. 5,220,562 to Takada et al., entitled Bridge Apparatus And A Communication System Between Networks Using The Bridge Apparatus, U.S. Pat. No. 5,220,563 to Grenot et al., entitled Device For The Transmission By An Asynchronous Network, Notably An ATM Type Network, Of Signaling Data, Channel By Channel, Assembled In A Multiframe Transmitted Synchronously In Out-Of Band Mode, U.S. Pat. No. 5,280,476 to Kojima et al., entitled Communication Control System Using An Asynchronous Transfer Mode Network, U.S. Pat. No. 5,457,684 to Bharucha et al., entitled Delay-Less Signal Processing Arrangement For Use In An ATM Network, U.S. Pat. No. 5,483,527 to Doshi et al., entitled Terminal Adapter For Interfacing An A TM Network With A STM Network, and U.S. Pat. No. 5,436,899 to Fujino et al., entitled High Performance Digitally Multiplexed Transmission System.